The present invention relates to improvements in gas turbine engines and nacelles therefor and, more particularly, to a novel gas turbofan engine which exhibits lower noise levels, improved fuel consumption, greater reliability, easier maintainability, easier replaceability, and improved thrust reversal over prior art gas turbofan engines.
Considerable attention has been devoted to developing a gas turbine engine which is quiet, clean and economical to operate. Significant improvement has been made in fuel consumption and noise levels of gas turbine engines over the past decade. Accordingly, a new family of high bypass, large diameter turbofans have recently been introduced into service. These engines have demonstrated noise levels and fuel consumption characteristics far superior to prior art gas turbine engines. The reduced noise levels of such high bypass turbofan engines is attributable to the reduced exit velocities of airflow pressurized by the fan. Though far more quiet than prior art gas turbofan engines, the recently introduced high bypass turbofan engines have higher noise levels than are desired. Therefore, Government regulatory agencies are applying ever more stringent requirements on newly certificated commercial aircraft. The objectionable noise levels in such engines generally result from the high tip speeds of the large diameter fan blades required to efficiently pressurize the bypass duct flow. This is in contrast to the turbojet or low bypass ratio turbofan engines in which the dominant noise source results from the discharge of the hot core gas stream through its propulsive nozzle.
It is, therefore, a primary object of the present invention to provide an economical, easily maintained gas turbine engine with improved noise levels.